For the past decade, ophthalmic surgeons have tried several methods to correct preexisting astigmatism during cataract eye surgery, including making incisions into the cornea to alter the shape of the eye. Now due to the unique design of toric intraocular lenses (IOL), astigmatism can be reduced or corrected without further surgical intervention. A tonic IOL restores focus to the eye when the natural lens or cataract is removed, but it is also designed to correct preexisting astigmatism using the same technology that has been successfully used in contact lenses.
Before the surgery, the amount of corneal astigmatism that needs to be corrected must be determined. In general, the procedure is as follows:                1. Pre-Operative Examination (Keratometry, Corneal Topography, Slit Lamp)        2. Calculation of IOL orientation        3. IOL Selection        4. Surgical insertion of toric IOL and alignment according to pre-calculated axis        
The success of such procedures depends in part upon the angular accuracy of the IOL alignment. All of the above steps have the potential to introduce a certain degree of error resulting in under-correction of astigmatism. However, a dominant source of error is the misalignment of the toric IOL according to the calculated angular value after it is inserted into the anterior chamber of a patient's eye during the cataract procedure. This may be, for example, due to the fact that the calculated IOL angle is based on measurements conducted with the patient sitting upright (pre-op setup) and alert, while during surgery the patient is in the supine position where cyclorotation occurs and under the influence of local anesthetic. Each degree of angular error may cause a 3.3% loss of astigmatic correction by the toric IOL. Thus 10° of error may cause a 33% reduction in the effect of the toric IOL, which is equivalent to using a spherical lens without astigmatism correction.
In order to avoid error due to the cyclorotation effect, there are currently several techniques to mark the eye with the meridian and pre-calculated IOL axis of alignment during the pre-operative examination. These techniques typically require the surgeon to place reference marks at the 3-o'clock and 9-o'clock meridians at the limbus utilizing markers or puncturing devices. Markings made by markers may be inaccurate, and may wash away or drift. Furthermore, puncturing the cornea is invasive and carries considerable risk of infection and/or other side effects.